nightcape1
Smash Apprentice
Not sure how well known this is, but instead of playing through SSE, you can unlock Sonic by logging a combined vs. playtime of 20 hours. Basically, the same way you unlocked Mewtwo in melee. I just thought that some character might be unlocked that way, so I plugged in all my controllers and left my game on all night in an infinite brawl, and when I woke up and reset the match, Sonic appeared.